On Mon, 15 Jan 2001, Benjamin Scott <[EMAIL PROTECTED]> wrote:
> On Sun, 14 Jan 2001, Karl J. Runge wrote:
> > Does anyone have an estimate how many users a satellite based ISP such
> > as starband.com can support?
>
> It would depend on a number of factors, including but not limited to:
>
> - How much bandwidth each user wants
> - Total radio spectrum available to said ISP
> - How much data throughput they can cram into said spectrum
> - Number of satellites they have
> - How well they can focus their transceivers (at both ends)
> - Bandwidth of return signal between the satellite and their ground station
>
> I don't think there is an easy answer to this.
Agreed.
I am not a network engineer, but I have a simple back of the envelope
model for estimating download bandwidth sharing. Without getting into
the details, the contraint that always seem to pop up is the intuitive
one:
B > N * (D / secs in a day)
where B is the total bandwidth of the pipe, N the number of users, and
D the number of bytes a user downloads a day. (It is a very simple
model that assumes a user's request are spread randomly thruout the
day: apply a fudge factor to correct for peak-vs-trough load,
correlations, safety factors, etc).
This same constraint pops up even for insuring that each customer gets
the personal download bandwidth "b" promised to him (ask me off list if
interested...). People with the background, please feel free to correct
me, but remember this is back of the envelope.
Anyway it seems to work for, say, Cable modem b/w sharing. I seem to
recall a single TV channel (6MHz wide <-> 40 Mb/s) can support about
1000-2000 users. Assuming a "fudge factor" of 5 this yields a D of
40MB. Which I guess is about right...
So, this would suggest a satellite ISP company buying up 500 TV
channels worth of bandwidth (i.e. like a satellite TV company), could
support 2000 * 500 = 1 million customers. I guess that could be
profitable... (but I am definitely not a businessman!) The other issues
Ben brings up would likely lower the number, by how much I don't know.
That is download, for upload I am a bit confused how that works with
the satellite system. Do the customers send their data in "time slots"
as in cable modem? At 2000 users per TV channel I suppose that would
work... (the system could possibly use GPS to get the customers clocks
accurately synchronized?)
Oh well, I hope the technology does prove to be scalable. Maybe someday
even I'll have a vacation cabin out in the sticks somewhere ;-)
Best,
Karl
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